Nanocrystal bonding is an important phenomenon in crystal growth, and nanoscale welding. Here, we show that for gold nanocrystals bonding in solution can follow two distinct pathways: 1) coherent, defect-free bonding occurs when two nanocrystals attach with their lattices aligned to within a critical angle; 2) beyond this critical angle, defects form at the interfaces where the nanocrystals merge. The critical misalignment angle for ~10 nm crystals is ~15o in both in-situ experiments and full-atom molecular dynamics simulations. Understanding the origin of this critical angle during bonding may help us predict and manage strain profiles in nanoscale assemblies, and inspire techniques towards reproducible and extensible architectures using only basic crystalline blocks.